I have a feeling that Whedon will not return for A3--he's going to be completely burnt out from 6 straight years of working with Marvel, and he's also probably going to want to do other (his own) projects, no matter how much money Disney throws at him.

Of course, we can't see the future so we don't know for sure, but in the case that Whedon does not return to direct A3, who would you want to see taking the reins of the franchise?

I think Marvel will make it sure that he will comeback for Avengers 3. And if Joss Whedon spent 7 years of his life working for his TV show Buffy. I don't see how its harder for him to release an Avengers movie in every 3 years. He's not even doing all the work like writing/directing for the other MCU films, And he and Marvel usually plan things way ahead of time.

Whedon would have spent years by then building up Thanos. He is not going to walk away during the climax of something he has been building up for a long time. He might leave after A3 but I don't see him leaving prior to A3, unless he gets into a big conflict with Marvel.